fighting has already ripped apart the country's largest city, aleppo. that's where arwa damon takes us through an exclusive look in parts of that city now turned into a war zone. >> reporter: aleppo's old city has not seen such devastation since occupied by the mongol invaders centuries ago. this mosque, for example, dates back to 1315. this is syria's rich cultural heritage, and now everywhere we look it's been scarred by war. once bustling, winding streets now a maze of ever shifting front lines. overhead the thundering of fighter jets. lodging for caravans down the aging rising ruins. for more than three millennium aleppo has been a crossroads for traders. we hurry through the courtyard of a traditional home. streets are strung across streets to block snipers line of site sight. a unit of fighters reports people's names and license plates. only those who have shops here are allowed through. abu says they're trying to clamp down on robberies. he says he shows us the list, the highlighted names have cleared out all their possessions. in one market a sh